1. Field of the Invention
This invention relates to an improvement in the technology for processing data remotely, and more particularly to the technology for using easily a plurality of databases each having different data structure from each other and for the technology for using agents efficiently even when a connection is difficult to establish while a terminal is moving.
2. Description of the Related Art
Recently, with the advance of the mobile communication technology and the miniaturization of a data processing apparatus, mobile computing has rapidly become popular. Mobile computing, which usually refers to the technology allowing a user to use a portable computer outside the office, also refers to the technology allowing the user to remotely access, over a telephone line from outside the office, to utilize a computer environment in the office.
One of mobile computing applications is the technology allowing the user to connect to the host system of a network and the like from the terminal over a telephone line and to access a database via a connection node such as a World Wide Web (WWW) server. With this technology, the user specifies a search condition in a Web page to search the database. Then, the search result is displayed in a new Web page. During this search, data is transferred between the user and the network in Web pages which are the smallest units (sessions) of data transferred between them at a time. As compared with a conventional client-server system, the sessions used during the transfer of Web pages are much smaller.
For this reason, searching a database with the use of Web pages is considered to be best for mobile computing in which the line connection is apt to be unstable. However, depending upon the load on the connection nodes via which a connection is established or on the database search method to be used, it may take long from the time a search request is issued to the time the result is displayed, sometimes requiring the user to stay connected to the host system for several minutes. And, once the connection with the host system is broken during the transfer of data, all the Web pages must be re-displayed.
To reduce the time during which the user must stay connected to the host system, a so-called mobile agent, a program sent from a portable terminal to the host system, is used. With the mobile agent, the user can connect the terminal to the host system where a desired database is provided and, once the agent having a processing procedure included is sent from the terminal to the host system, disconnect from the host system. The agent sent to the host system searches the database according to the given procedure and, when the result is obtained, either the portable terminal calls up the host system, or vice versa, to return the result to the user's terminal. The use of this mobile agent eliminates the need to stay connected to the host system during database search operation, making it possible to reduce the amount of communication.
The problem with the related system described above is that it is difficult for the user to utilize a plurality of databases. That is, with the conventional Web-page based search or the mobile agent which is designed to access a single database, it is difficult to access two separate databases at a time. In this case, it should be noted that "two separate databases", though dissimilar in data structure (schema) formally, contain data similar with each other in content or attribute in most cases. For example, consider two personnel information databases developed by two separate divisions of a company. In this case, searching for employees satisfying specified conditions or having specified qualifications requires the user to search the two databases dissimilar in data structure.
That is, locally-generated data should be stored in local databases to prevent database sizes and loads from increasing; on the other hand, the plurality of databases sometimes contain data to be shared among them.
Thus, searching a plurality of databases, each with dissimilar data structure with each other, requires the user to change the search request format according to the data structure of each database. Not only does the user find it bothersome to switch among a plurality of databases and change the request format manually but also the communication time becomes longer. Therefore, searching a plurality of databases is not suitable for mobile computing. In addition, the conventional agent does not access a plurality of databases, nor does it work with a plurality of data structures dissimilar with each other.
Another known access technology is that two separate databases have the same record structure to allow access to the two databases. However, this function cannot be combined with the conventional agent which does not move within the host system to access a plurality of databases. In addition, the use of the common record structure requires that the databases be designed to have the common record structure from the database development stage. This is cumbersome and cannot be applied to existing databases.
For connecting the host system and terminals such as Personal Hadyphone System (PHS) telephones used in a communication mode not intended for mobile communication, it is difficult to access databases while moving from one location to another. That is, although the user who remotely accesses a database outside the office must move frequently in many cases, the communication method, such as that used by the PHS, does not give the user stable connections while the user is moving from one location to another. This is because, in the PHS system where the output from an antenna base station is very weak, the connection is frequently broken if the user changes his or her locations frequently. This means that the user must stay within an area where the radio wave is strong sufficiently during communication using a PHS telephone.
On the other hand, the user using the conventional mobile agent technology sends an agent to the host system, one at a time, and receives the result. Therefore, when making a plurality of search requests to get many pieces of information from databases, the user must send agents, and receives results, continuously while staying connected to the line. The result is that the communication time becomes long and, therefore, the user cannot leave the place during that time.
Furthermore, in a system where the conventional mobile agent technology is used, even when the host tries to send back a result to the terminal immediately after the result is obtained, the called terminal sometimes cannot respond while the user carrying it is moving in case of the PHS system. Thus, with the conventional mobile agent, the user finds it difficult to use databases in a communication mode not intended for mobile communication.
This invention seeks to solve the problems associated with the related art described above. It is an object of this invention to provide a technology which makes it easier for the user to use a plurality of databases each with dissimilar data structure with each other. It is another object of this invention to provide a technology which allows the user to use databases even over a communication line via which mobile communication is difficult.